Laser marking process

ABSTRACT

A manufacturing method for sapphire crystal material is disclosed, including a laser-etched bar code formed into the interior of the sapphire crystal material. The laser-etched bar code may be associated with one or more manufacturing parameters or other manufacturing data. The sapphire crystal may be used to create a cover sheet for use with a display screen of a portable electronic device.

CROSS-REFERENCE TO RELATED APPLICATION APPLICATIONS

This application is a reissue patent application of U.S. Pat. No.9,600,694, issued Mar. 21, 2017 and titled “Laser Marking Process,”which is a non-provisional patent application of and claims the benefitto U.S. Provisional Patent Application No. 62/010,619, filed Jun. 11,2014, and titled “Laser Marking Process,” the disclosure disclosures ofwhich is are hereby incorporated herein by reference in its entiretytheir entireties.

TECHNICAL FIELD

The described embodiments relate generally to methods of manufacturing acrystal material. More particularly, embodiments relate to forming alaser mark in an internal portion of a sapphire material.

BACKGROUND

Recent advances in portable electronics allow portable electronicdevices to be carried most anywhere. As such, these devices may besubjected to various environments and conditions which are hostile tothe materials used to construct these devices. In particular, the outersurface of a portable electronic device, such as the screen portion, maybe subjected to scratching or surface abrasions. Traditionally, glasshas been used to protect portions of the outer surface such as thescreen portion, which may become scratched or broken when subjected tonormal use.

In some cases, a harder and more scratch resistant surface, such assapphire may be advantageous as compared to traditional glass materials.However, the use of sapphire as a component may present challenges overconventional silicate glass. In particular, the quality of sapphire as araw material may be highly dependent on manufacturing conditions. Insome cases, it may be beneficial to track the manufacturing conditionsor process parameters as a sapphire component is being made.

Further, use of synthetic sapphire crystal, as compared to glass, infabricating components for electronic devices may result in much greatervariability of the resultant material and defects from the manufacturingprocess. In order to ensure product quality control it may be useful totrack information such as manufacturing characteristics related to eachstep of the process in order to improve process operations and provideproduction control. Because the surface of the sapphire material isremoved multiple times during the production process, surface marking ofthe sapphire can be unsuitable for use as a tracking method.

SUMMARY

Some example embodiments are directed to a laser mark that is createdwithin a sapphire material using a laser beam. The laser mark mayinclude information encoded in a small bar code or other graphicalelement that is formed within a sapphire sheet. The laser mark may beused to track the sapphire component, the device, and/or originalsapphire boule.

Some example embodiments are directed to a method of manufacturing asapphire component of a portable electronic device. The method mayinclude forming a laser mark on a portion of the interior of thecomponent between the upper surface and the lower surface. Forming ofthe laser mark may be performed when one of the upper and lower surfacesare substantially unpolished. The laser mark may include encodedinformation. After forming the laser mark, the upper and lower surfacesof the component may be polished. In some embodiments, the encodedinformation includes information associated with the growing of anassociated synthetic crystal boule. In some cases, the laser mark isdetectable after the polishing.

In some embodiments, the upper surface of the sheet is substantiallyunpolished and forming the laser mark includes covering at least aportion of the upper surface with a liquid having an index of refractionapproximately equal to an index of refraction of the sheet. The lasermark may be formed while the portion of the upper surface is coveredwith the liquid. In some embodiments, the sheet includes an uneven uppersurface and forming the laser mark includes providing a lens adjacent tothe upper surface, and forming the laser mark using the lens. In someembodiments, forming the laser mark includes focusing a laser beam at alocation between the upper and lower surfaces to alter an index ofrefraction of the sapphire component at the location. In someembodiments, the forming of the laser mark includes etching an interiorportion along a neutral axis of the sheet between the upper surface andthe lower surface.

In some embodiments, forming the laser mark includes etching a bar codeinto the portion of the sapphire component. The bar code may encodeinformation associated with a manufacturing condition of the growing ofan associated crystal boule.

Some example embodiments are directed to a cover sheet for a portableelectronic device. The cover sheet may be formed from a syntheticcrystal sheet having an upper surface and a lower surface. The crystalmaterial may also include a laser-etched mark between its upper surfaceand lower surface. In some embodiments, the cover sheet is substantiallytransparent to light and the marking includes information associatedwith a manufacturing condition of the synthetic crystal. In someembodiments, the synthetic crystal is sapphire.

The laser-etched mark may be located along a neutral axis of the sheet.The marking may be formed substantially perpendicular to the uppersurface. The laser-etched mark may be substantially undetectable to anunaided eye.

Some example embodiments are directed to a portable electronic deviceincluding a housing, a display disposed within the housing, and a coversheet attached to the housing and disposed over the display. The coversheet may include a synthetic crystal material having an upper surfaceand a lower surface, and a marking within the sheet between the uppersurface and the lower surface. The marking may include informationassociated with a manufacturing condition of the synthetic crystal.

In some embodiments, the size of the laser-etched mark can be minimizedsuch that the mark is machine readable and sufficiently small that it issubstantially not visible to the naked or unaided eye. For example,laser mark may not be readily detected by a person without the use ofexternal optics (e.g., lenses) or special, illumination techniques. Insome embodiments, the mark is approximately 126μm×126μm.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be readily understood by the following detaileddescription in conjunction with the accompanying drawings, wherein likereference numerals designate like structural elements, and in which:

FIG. 1 shows a boule of synthetic sapphire crystal divided into aplurality of brick portions and further divided into sheets sawed fromthese brick portions;

FIG. 2 is a side view of a laser etching a bar code on a sapphire sheet;

FIG. 3 shows a top view of a bar code etched in a sapphire sheet;

FIG. 4 is a side view of a laser etching a bar code on a sapphire sheetthrough a liquid layer;

FIG. 5 is a side view of a laser etching a bar code on a sapphire sheetthrough a lens;

FIG. 6 is a view of a smartphone with a sapphire glass display window;

FIG. 7 is an alternate embodiment showing a laser etching a bar code ina brick of sapphire crystal material;

FIG. 8 is a side view showing a light source illuminating a bar code ina sapphire crystal; and

FIG. 9 is a flow chart illustrating a manufacturing method for sapphirecrystal displays.

DESCRIPTION

Reference will now be made in detail to representative embodimentsillustrated in the accompanying drawings. It should be understood thatthe following descriptions are not intended to limit the embodiments toone preferred embodiment. To the contrary, it is intended to coveralternatives, modifications, and equivalents as can be included withinthe spirit and scope of the described embodiments as defined by theappended claims.

As described herein, a laser mark may be formed within a transparentmaterial, such as sapphire. In some embodiments, a laser mark is formedby focusing laser energy within the bulk of the material to locallydestroy the structure. The local destruction of the structure may resultin a change or alteration in index of refraction of the material whichcan render the locally-destroyed area optically or machine detectable,but difficult to see without optical aids or specific lightingconditions.

In some embodiments, the laser mark is formed by damaging or alteringthe crystalline structure of sapphire in a very small region to create aregion having a slightly different optical index. In some embodiments, alaser is used to alter the index of refraction of the material over alocalized region. In some embodiments, regions created in this fashionmay further reduce the visibility of the mark from common viewing anglesof a user while still preserving the detectability of the bar codemarking via controlled orientation lighting and imaging apparatus.

By placing a laser mark, such as a small bar code, within the material,the mark may survive unaltered through a series of surface removalprocess steps. Also, by locating the laser mark on or near the neutralaxis of the material, a reduction in stress-related breakage of aresulting part, such as a display or cover glass made from the sapphirewafer, or a camera window, may be achieved.

In practice, creating this type of mark can be very challenging. Forexample, the surface of the sapphire at the early process stages wherethe laser mark is to be applied may not be polished, but rather roughand diffuse, which may tend to scatter laser energy. One approach toovercome the difficulty of focusing a laser beam within the sapphirecrystal surface is to use a surface fluid having a refractive indexsubstantially matching that of the sapphire. In some embodiments, thisprovides a uniform surface, thereby reducing surface scatter andimproving laser light transmission into the sapphire crystal.

In some embodiments, a laser mark may include encoded information in,for example a bar code or other optically encoded data. In these cases,laser mark can be used to track key manufacturing and materialprocessing information through the manufacturing process and eventhrough the service life of the product. The laser mark can be used toidentify potential problems, adapt manufacturing processes, and improvereliability over time. The laser mark or bar code can also be used toprovide a simple check to ensure components are authentic or originatefrom an authorized vendor. Furthermore, because the cost of sapphirecomponents may be high, reducing the rework of sapphire parts, evenafter a display lamination process, may be important for cost recovery.A laser mark or bar code may be useful in this scenario because therework may involve re-polishing of the sapphire surface. A laser markmay also be useful to track the repair history of the part. For example,repeated replacement of the part may indicate user abuse or other factoror cause of frequent repairs. A laser mark internal to the sapphirematerial may be less susceptible to obfuscation caused by polishing and,therefore may be advantageous to ensure accurate tracking of the reworkhistory for a specific sapphire part.

Techniques and methods described herein may be particularly well suitedfor manufacturing components from a sapphire material, including a coverglass or other display surface, a button, a window (for example, awindow disposed over a camera or camera lens), a lens, an input surface,or a portion of an exterior housing. In particular, the followingtechniques may improve the manufacturing process for a sapphire part ascompared to some processes used to manufacture traditional glasscomponents. For conventional glass, the material properties and incomingquality of the glass used for display covers, windows, external surfacesand the like is of such a high consistency that a basic inspection forgross defects may be sufficient. Additionally, the consistency ofstrength and cosmetic quality of finished glass parts may be relativelyhigh negating the need for manufacturing controls and parametertracking. In addition, for conventional glass elements, the chemicalstrengthening process may be the dominant factor for increasing strengthin a consistent production process. Because the degree of strengtheningmay be checked on all parts, important quality measures or parametersmay be gathered and recorded toward the end of the manufacturingprocess.

FIG. 1 shows a process for dividing a boule 11 of synthetic sapphirecrystal into a group of brick portions 12. That is, the syntheticsapphire crystal boule is grown and various brick portions 12 may be cutfrom it. Sheets 13 may then be sliced or sawed from these brick portions12. In a typical process, as many as 16 bricks 12 may be cut from asingle boule 11, although this depends on the size of the boule andbricks. Depending upon the size of the bricks, a set of sheets 13 may becut from each brick 12. Each time the sapphire crystal is cut, a newsurface is created. Thus, placing a marking on the cut piece, whether itis brick 12 or sheet 13, at each step of the process may not be feasibleor practical.

A bar code, logo, alphanumeric string, graphic, QR code, or other code(collectively, “bar code”) 14 may be placed on an interior portion ofeach sheet to identify that particular piece of material andmanufacturing characteristics associated therewith. For example, the barcode 14 may identify the manufacturing characteristics, including thedate of manufacture of the crystal, the location of manufacture of thecrystal, and manufacturing parameters that may help determine thequality or origin of the material. Such information may aid in laterquality and production control processes and assist in rework,refurbishment or repair processes as discussed herein. For example,knowing the origin of the crystal may allow comparison with other piecesmade from the same boule. It should be appreciated that the bar code 14may include substantially any information desired such as a point oforigin, company data, information identifying shipping and/or handlingof the crystal or components formed therefrom, although manufacturingcharacteristics are discussed herein.

Bar code 14 may be formed with the material, which, in one embodiment issapphire, using a laser-based process. Referring to FIG. 2, a side viewof a laser beam 15 is shown penetrating an upper surface 23 of asapphire component, such as sapphire sheet 13. Sapphire sheet 13 may beone of sheets described above in FIG. 1, although it should beappreciated that any sapphire component may be encoded as describedherein. Accordingly, the term “sapphire sheet” is intended to embraceother forms and geometries of sapphire components.

The location at which the focal point 17 of laser beam 15 intersectswithin sapphire sheet 13 is where the energy density of laser beam 15 ishighest and it is this point where the internal crystal structure may bealtered by laser beam 15 so as to leave a series of marks to form barcode 14. In some embodiments, laser beam 15 changes the refractive indexof the sapphire material at focal point 17 such that the marks left bylaser beam 15 may not be visible to the unaided eye but are detectablewith the proper optical equipment. In some embodiments, the bar code 14is substantially undetectable to the unaided human eye. In someembodiments, the bar code 14 is placed on a neutral axis 19 of sapphiresheet 13. By placing it on the neutral axis 19, bar code 14 may not bedetectable to the unaided eye and the laser marking does not compromisethe stress tolerance of sapphire crystal sheet 13.

Referring to FIG. 3, a top view of sheet 13, shown looking through uppersurface 23, illustrates bar code 14 etched inside sheet 13. Although thesimplified representation of the bar code 14 in FIG. 3 is depicted as aseries of lines (characters 18), the bar code 14 may include a1-dimensional, 2-dimensional, or 3-dimensional pattern of shapes thatencode information, such as characters or symbols. Bar code 14 coversapproximately 126μm×126μm in which characters 18 can be placed to trackthe origin of sheet 13 for quality control and manufacturing processpurposes. In some embodiments, the bar code 14 may include up to 31characters, although the exact number of characters, as well as thedimensions of the code, may vary between embodiments. The bar code 14may be used to track the source or origin of the sheet in terms of whichboule it came from, the date of manufacture, the location of the furnaceor other equipment that was used, or other manufacturing parameterswhich could later be used to improve the manufacturing process. Thisvaluable information may be lost if the bar code was placed in alocation in which the bar code would not be preserved such as on anouter surface of a sheet or brick. In some embodiments, the laser markor bar code can also be used to provide a simple check to ensurecomponents are authentic or originate from an authorized vendor.

With respect to FIG. 4, in order to improve the laser etching process ofsapphire sheet 13, the sheet 13 may be placed in an enclosure 21 and aliquid 22 disposed on at least a portion of upper surface 23 of sapphiresheet 13. As mentioned above, the sawing of sheet 13 from brick 12 mayresult in upper surface 23 being uneven as is shown in FIG. 4. Liquid 22may be selected so as to have a light refractive index approximatelyequal or substantially matched to that of the sapphire sheet 13. Byplacing liquid 22 on the uneven surface 23 of sheet 13, the laser beamused to etch the internal surface may enter the part via a uniformsurface 24. The uniform surface 24 may not diffuse laser beam 15 as mayotherwise occur if laser beam 15 were directed at uneven surface 23without refractive liquid 22. In one embodiment, liquid 22 is placedover at least the portion of the sheet 13 through which laser beam 15 isdirected to form the laser mark on the interior portion of sheet 13.

Referring to FIG. 5, a lens 25 may be placed adjacent to surface 23 tofocus the laser beam within the material and minimize diffusion causedby the uneven surface 23. Without lens 25, energy from the laser beam 15may be dissipated by an uneven surface 23 and cause damage at thesurface 23 or affect the etching operation. By using lens 25, the energyof laser 15 may be relatively dispersed at the surface 23 and relativelyconcentrated at the focal point 17 inside the sheet 13. This may improvethe efficiency of a laser marking operation. The use of lens 25 may bein addition to, or in place of, the liquid layer described with respectto FIG. 4 in order to focus laser beam 15 at the location where bar code14 is to be formed.

FIG. 6 depicts an example portable electronic device, specifically asmartphone 26, incorporating a marked sapphire element as discussedherein. The portable electronic device could also be a wearable device,health monitoring device, tablet computer, laptop computer, media playeror other electronic device as the embodiments disclosed herein are notlimited to a smartphone. Smartphone 26 includes a housing 27 and variouscontrol inputs 28 used to provide user input. In some embodiments, acover sheet is attached the housing 27 via a pressure-sensitiveadhesive, fastener, or other attachment technique. The cover sheet 16which, in some embodiments, may be sapphire crystal sheet, as describedherein. Cover sheet 16 may include bar code 14 and may be manufacturedin accordance with various embodiments described herein. Bar code 14 maybe placed in an inconspicuous location on the cover sheet 16 so as notto be readily perceived by a user of the portable electronic device.

Referring to FIG. 7, bar code 14 may be placed directly into brick 12rather than being placed into sheets 13 after they have been cut frombrick 12. The boule 11 of synthetic sapphire crystal is shown dividedinto a plurality of brick portions 12. As with the embodiment describedin FIG. 1, the synthetic sapphire crystal boule 11 is grown and variousbrick portions 12 may be cut from it. Prior to sheets 13 being sawedfrom these brick portions 12, bar code 14 may be placed on the interiorportions of each brick 12 at various portions coinciding with locationof the sheets 13 to be cut from the brick portion 12. In someembodiments, the bar code 14 is formed along a plane that isperpendicular or otherwise transverse to the side surface of brickportion 12 such that it will also be perpendicular to the neutral axis19 and upper and lower surfaces on each sheet portion. In suchembodiments, bar code 14 may be readable from an end surface 29 of sheet13 rather than from an upper surface 31 of sheet 13 which upper surfacecoincides with a user's view of a cover sheet 16 in smartphone 26. Insome embodiments, a user may have even more difficulty visuallydetecting bar code 14 with his or her naked eye making bar code 14potentially more useful as an anti-counterfeiting measure. In someembodiments, viewing the bar code 14 would require disassembly of coversheet 16 front smartphone 26 in order to view the bar code from the sideof cover sheet 16.

FIG. 8 is a side view of a sheet 13 of crystal sapphire material withbar code 14 included therein. A light source 32, which, in oneembodiment, may be a high intensity light source, propagates light rays33. Light rays 33 enter sheet 13 generally parallel with the orientationof bar code 14 but some of light rays 33 are scattered normal to theorientation of bar code 14 so as to be detectable by an observer, eitherwith an unaided (naked) eye 34, or with optical equipment 35. In thisway, bar code 14 may be read, either during the manufacturing process,or after sheet 13 is processed into cover sheet 16 in order to identifymanufacturing characteristics of the sheet including the source ororigin of the original sapphire crystal from which the resulting coversheet 16 was made.

FIG. 9 is a flow chart of a sample sapphire component manufacturingprocess 100. The example process 100 may be used to create ormanufacture a cover 16, as described above with respect to FIG. 6.Process 100 may also be used to create other types of sapphire partshaving a laser mark formed or embedded within the sapphire material.

In operation 102, a synthetic sapphire crystal boule is grown (e.g.,item 11 of FIG. 1). One technique for manufacturing sapphire may includeuse of a sapphire seed crystal which is dipped into a cruciblecontaining molten alumina, and then slowly withdrawn upward at a rate ofone to 100 mm per hour. The alumina may crystallize on an end, creatinglong carrot-shaped boules of large size up to 200 kg in mass. In somecases, the manufacturing processes may be imprecise or variable, whichmay introduce imperfections or variations into the boule. Thus, in somecases, it may beneficial to be able identify and track both defectiveand high quality boules. In some embodiments, the boule identificationmay be used to locate high quality material. In some embodiments, theidentification can also be used to troubleshoot the manufacturingprocess by tracking potential material issues all the way back to theboule creation operation 102.

In operation 104, a boule is cut into bricks and at operation 106 thosebricks are sliced into sheets (e.g., item 13 of FIG. 1). During theseprocess operations, as with the boule manufacturing process, defects canbe introduced into the bricks and sheets. Again, it may be beneficialthat any such defects be identified so that errors of the same type arenot repeated. By identifying the source of a cover sheet which is foundto have a certain defect, it may be determined whether other coversheets from the same boule processing batches suffer from the samedefect and the boule processing may thus be improved. In someembodiments, the sapphire sheet may have rough saw-cut surfaces due tothe slicing operation, which may be difficult to mark using traditionalsurface-marking techniques.

In operation 108, a laser mark is formed. In some cases, a bar code isformed using a laser-based process into an inner portion of the sheetsand/or bricks formed in operations 104 and 106, respectively. The lasermark may include information associated with the growing of a syntheticcrystal boule (e.g., operation 102). For example, the manufacturingconditions or parameters of the boule from which the brick and sheet,and later the cover sheet made therefrom, may be encoded into a bar codethat is formed as a laser mark on an interior portion of the sheet.Further, the source or origin of the sapphire crystal, including thefurnace, manufacturing facility, and time of manufacture may beassociated with the bar code. Other manufacturing conditions orparameters, including the temperature, crystal growing conditions, orother manufacturing data may be associated with the bar code. The lasermark may be used to track the part and/or facilitate quality control. Insome embodiments, the information contained in the laser mark may becritical in the quality control process in order to identifymanufacturing or process operations which can be improved as discussedabove.

In some embodiments, operation 108 is performed before any substantialpolishing has been performed on the surface of the sheet. For example,the bar code may be formed while the surface of the sheet is still roughfrom the slicing operation of operation 106. As described previouslywith respect to FIGS. 4 and 5, the formation of a laser mark may befacilitated by using an index matching liquid and/or optical lens toassist in focusing the laser beam within the sapphire material. In otherembodiments, operation 108 may be performed after polishing and/or othermachining operations are performed on the sheet surface.

In operation 110, the sliced (and marked) sheets may be subjected tofurther processing, including polishing, grinding, and/or lapping thesurfaces. In some cases, the sliced sheets are polished to a high gradesurface finish in order to produce cover sheets (e.g., item 16 of FIG.6). In some embodiments, because bar code is formed within an interiorportion of sheet, the polishing, finishing or lapping processes do notremove or otherwise obscure bar code. If a mark or traditional printingwere to be formed onto the surface of sheets, the polishing of thosesheets could obliterate, or at least partially obscure the mark. Also,by forming the bar code on the interior of the sheets between upper andlower surfaces, bar code remains intact and may be read as describedherein. Thus, useful information relating to the growing of boule aswell as the subsequent processing of bricks and sheets may be preserved.At operation 112, the processed sheets (e.g., cover sheets) may beincorporated or installed into a portable electronic device. In someembodiments, operation 112 is optional or performed as part of aseparate manufacturing process. For example, the cover sheets may bemanufactured separately and then shipped or transferred to anotherfacility for installation into a portable electronic device.

The inclusion of bar code 14 in each cover sheet 16 permits qualitycontrol in the finished cover sheets and may be used to improve themanufacturing process of those cover sheets. While bar code 14 mayadvantageously be used to improve the manufacturing process for sapphirecrystal, it can be appreciated that bar code 14 may also aid incounterfeit detection of display covers (or other components) that havebeen used to replace the original cover. In addition to counterfeitdetection, bar code 14 could be used in tracking reworked cover sheetsor displays. That is, where a user of a portable electronic devicereturns that device to the manufacturer because of defects in the screenportion of the device, bar code 14 could be read to determine origins ofthe display and whether it was part of the original electronic device orwhether it was added after purchase by the user. If particular defectsoccur repetitively in displays with similar bar codes then themanufacturer may determine that a particular batch of sapphire crystalmay be defective and take corrective measures to avoid similaroccurrences in the future. If the display screen was damaged by theuser, identification information would also be useful to determine ifthis user has damaged previous display screens. In some embodiments, thelaser mark or bar code can also be used to provide a simple check toensure components are authentic or originate from an authorized vendor.

While the disclosed embodiments have been described primarily withrespect to synthetic sapphire crystal glass production, it can beappreciated that application of the laser identification processdisclosed herein may find application in any number of processes and inparticular with respect to the production of transparent glass productsusing a variety of materials including ordinary silicate glass basedproducts. In addition, while the disclosed embodiments have utilized aparticular type of fast laser etching process, it should be expresslyunderstood that any suitable laser etching process for inscribing orforming a bar code on the interior of a transparent glass like materialmay be utilized.

The foregoing description, for purposes of explanation, used specificnomenclature to provide a thorough understanding of the describedembodiments. However, it will be apparent to one skilled in the art thatthe specific details are not required in order to practice the describedembodiments. Thus, the foregoing, descriptions of the specificembodiments described herein are presented for purposes of illustrationand description. They are not targeted to be exhaustive or to limit theembodiments to the precise forms disclosed. It will be apparent to oneof ordinary skill in the art that many modifications and variations arepossible in view of the above teachings.

What is claimed is:
 1. A method for manufacturing a cover sheet for adisplay of a portable electronic device, the method comprising: growinga synthetic single-crystal sapphire boule; cutting the synthetic singlecrystal single-crystal sapphire boule into a brick portion; slicing thebrick portion into a single-crystal sheet having an upper surface and alower surface; forming a laser mark on a portion of the interior of thesingle-crystal sheet between the upper surface and the lower surface andalong a neutral axis of the single-crystal sheet, wherein the laser markincludes encoded information; and after forming the laser mark,polishing the upper and lower surfaces of the single crystalsingle-crystal sheet to form the cover sheet.
 2. The method of claim 1,wherein the encoded information includes information associated with thegrowing of the synthetic single-crystal sapphire boule.
 3. The method ofclaim 1, wherein the forming of the laser mark includes focusing a laserbeam at a location between the upper and lower surfaces to alter anindex of refraction of the material at the location.
 4. The method ofclaim 1, wherein the forming of the laser mark is performed when one ofthe upper and lower surfaces are is substantially unpolished.
 5. Themethod of claim 4, wherein the upper surface is substantially unpolishedand the method further comprising comprises: covering at least a portionof the upper surface with a liquid having an index of refractionapproximately equal to an index of refraction of the single-crystalsheet; and forming the laser mark while the portion of the upper surfaceis covered with the liquid.
 6. The method of claim 1, wherein thesingle-crystal sheet includes an uneven unpolished upper surface and themethod further comprises: positioning a lens adjacent to the uppersurface; and forming the laser mark using the lens.
 7. The method ofclaim 1, wherein the forming of the laser mark includes etching a barcode into the portion of the single-crystal sheet, wherein the bar codeencodes information associated with a manufacturing condition of thegrowing of the synthetic single-crystal sapphire boule.
 8. The method ofclaim 1, wherein the forming of the laser mark includes etching aninterior portion along a the neutral axis of the single-crystal sheetbetween the upper surface and the lower surface.
 9. The method of claim1, wherein the laser mark is optically detectable after polishing theupper and lower surfaces.
 10. A cover sheet for a portable electronicdevice comprising: a sheet of synthetic single-crystal having an uppersurface and a lower surface; and a laser-etched mark marking formedwithin the synthetic single-crystal sheet between the upper surface andthe lower surface and along a neutral axis of the single-crystal sheet,wherein the single-crystal sheet is substantially transparent to lightand the marking includes information associated with a manufacturingcondition of the synthetic single-crystal sheet.
 11. The cover sheet ofclaim 10, wherein the marking is located along a neutral axis of thesingle-crystal sheet the neutral axis of the cover sheet is positionedhalfway between the upper surface and the lower surface.
 12. The coversheet of claim 10, wherein the laser marking is substantiallyundetectable to an unaided eye.
 13. The cover sheet of claim 10, whereinthe marking is formed in a direction that is substantially perpendicularto the upper surface.
 14. The cover sheet of claim 10, wherein thesynthetic single-crystal sheet is formed from sapphire.
 15. A portableelectronic device comprising: a housing; a display disposed within thehousing; a cover sheet attached to the housing and disposed over thedisplay, the cover sheet including: a synthetic single-crystal materialhaving an upper surface and a lower surface, and a laser-etched markmarking within the cover sheet between the upper surface and the lowersurface and along a neutral axis of the cover sheet, the markingincludes including information associated with a manufacturing conditionof the synthetic single-crystal material.
 16. The device of claim 15,wherein the manufacturing condition indicates the a repair history ofthe cover sheet.
 17. The device of claim 15, wherein the marking islocated along a neutral axis of the cover sheet the neutral axis of thecover sheet is positioned halfway between the upper surface and thelower surface.
 18. The device of claim 15, wherein the manufacturingcondition of the synthetic single-crystal material includes one or moreof: a manufacturing date, a manufacturing location; or a manufacturingparameter.
 19. The device of claim 15, wherein the marking issubstantially undetectable to an unaided human eye.
 20. The device ofclaim 15, wherein the synthetic single-crystal material is sapphire. 21.A method for manufacturing a cover sheet for a display of a portableelectronic device, the method comprising: forming a laser mark within achemically-strengthened silicate glass sheet, the laser mark positionedbetween an upper surface of the silicate glass sheet and a lower surfaceof the silicate glass sheet and along a neutral axis of the silicateglass sheet, wherein the laser mark includes encoded information; andafter forming the laser mark, polishing the upper and lower surfaces ofthe glass sheet to form the cover sheet.
 22. The method of claim 21,wherein the encoded information includes information associated with amanufacturing condition of the silicate glass sheet.
 23. The method ofclaim 21, wherein the forming of the laser mark includes focusing alaser beam at a location between the upper and lower surfaces to alteran index of refraction of the silicate glass sheet at the location. 24.The method of claim 21, wherein the forming of the laser mark isperformed when one of the upper and lower surfaces is substantiallyunpolished.
 25. The method of claim 24, wherein the upper surface issubstantially unpolished and the method further comprises: covering atleast a portion of the upper surface with a liquid having an index ofrefraction approximately equal to an index of refraction of the silicateglass sheet; and forming the laser mark while the portion of the uppersurface is covered with the liquid.
 26. The method of claim 21, whereinthe glass sheet includes an unpolished upper surface and the methodfurther comprises: positioning a lens adjacent to the upper surface; andforming the laser mark using the lens.
 27. The method of claim 21,wherein the forming of the laser mark includes etching a bar code intoan interior portion of the silicate glass sheet, wherein the bar codeencodes information associated with a manufacturing condition of thesilicate glass sheet.
 28. The method of claim 27, wherein the bar codeis within an area of 126 μm by 126 μm.
 29. The method of claim 21,wherein the laser mark is optically detectable after polishing the upperand lower surfaces.
 30. A glass cover sheet for covering a display of aportable electronic device, comprising: a chemically-strengthenedsilicate glass sheet substantially transparent to light and defining anupper surface and a lower surface; and a laser-etched marking formedwithin the silicate glass sheet between the upper surface and the lowersurface and along a neutral axis of the silicate glass sheet, thelaser-etched marking including information associated with amanufacturing condition of the silicate glass sheet.
 31. The glass coversheet of claim 30, wherein the neutral axis of the silicate glass sheetis positioned halfway between the upper surface and the lower surface.32. The glass cover sheet of claim 30, wherein the laser-etched markingis within an area of 126 μm by 126 μm.
 33. The glass cover sheet ofclaim 32, wherein the laser-etched marking is a bar code.
 34. The glasscover sheet of claim 32, wherein the laser-etched marking is a graphic.35. A portable electronic device comprising: a housing; a displaydisposed within the housing; and a cover sheet attached to the housingand positioned over the display, the cover sheet including: achemically-strengthened silicate glass material defining an uppersurface and a lower surface, the upper surface defining an exteriorsurface of the portable electronic device; and a laser-etched markingwithin the cover sheet between the upper surface and the lower surfaceand along a neutral axis of the cover sheet, the marking includingencoded information associated with a manufacturing condition of thechemically-strengthened silicate glass material.
 36. The portableelectronic device of claim 35, wherein the manufacturing conditionindicates a repair history of the cover sheet.
 37. The portableelectronic device of claim 35, wherein the neutral axis of the coversheet is positioned halfway between the upper surface and the lowersurface.
 38. The portable electronic device of claim 35, wherein themanufacturing condition of the chemically-strengthened silicate glassmaterial includes one or more of a manufacturing date, a manufacturinglocation, or a manufacturing parameter.
 39. The portable electronicdevice of claim 35, wherein the marking is substantially undetectable toan unaided human eye.
 40. The portable electronic device of claim 35,wherein the marking is a 2-dimensional pattern of shapes within an areaof 126 μm by 126 μm and encoding an identifier of the cover sheet.